With the development of electronic control circuits, and their adaption for use with electric motors and the like, there has developed a need and desire to mount these electronic circuits in close proximity to the motor. This enhances the utility of the electronics and results in a more compact design which is also more efficient and less expensive to manufacture. However, one significant problem with the association of these electronic circuits with an electric motor or the like is the deleterious effect that heat has on these devices. As is well known, electric motors can generate a significant amount of heat, and electronic components can be very heat sensitive, especially those power transistors or other switching devices which might be used to switch significant amounts of current to the motor windings.
In the prior art, heat sinks have been developed for the mounting of those higher power electronic components requiring heat sinking, but these heat sinks have generally been merely attached by bolting or screwing them onto the conduit box or inside the shell of the motor. Of course, the mounting of the heat sink can be critical in that some attention must be paid to dissipating the heat from the heat sink. Generally, this can be done by either exposing the cooling fins of the heat sink to a steady circulation of air or to the exterior of the enclosure, or by bringing the heat sink into close thermal contact with a surrounding enclosure. In some designs, the heat sink is coupled to the shaft which rotates it as the motor is operated. In other designs, the heat sink is covered but a steady draft of cooling air is blown over the heat sink. In still other designs, the heat sink is made of sufficient capacity to operate satisfactorily without exposure to exterior air. However, these designs are susceptible to heat build-up and must of necessity contain greater material and hence be more expensive than those designs exposed to exterior air.
The inventor herein has succeeded in developing two new heat sink designs and mounting for them which represents a dramatic improvement over the prior art in compactness of design, efficiency of operation, and ease in installing and removing the heat sink along with its associated electronic circuitry for repair or replacement thereof. In the first design, a generally circular PC board is mounted across the open face of a generally annular heat sink through the electronic leads of power transistors. As is known in the art, the power transistors are rigidly mounted by their cases to the heat sink and thermally coupled thereto to maximize the efficiency of operation of the heat sink, and the electronic leads from the power transistors are connected by soldering or the like to the PC board itself. By making no other physical connections between the PC board and the heat sink, a limited amount of flexure is permitted therebetween. Therefore, with this generally annular design, the heat sink and PC board is uniquely suited for insertion within the sleeve of an electric motor or the like by compressing the heat sink and then releasing it so that it "springs" against the outer shell of the motor sleeve and is held in place through spring tension. This is achieved by making the arcuate shape of the generally annular heat sink somewhat greater than the circular shape of the sleeve. Additionally, the heat sink is formed with a plurality of grooves or channels extending across the outer face thereof which can be filled with a suitable potting material or fixative to both fix the heat sink against the sleeve and to provide a closer thermal coupling between the heat sink and sleeve so as to improve the heat transfer characteristic therebetween. This improved coupling and heat transfer characteristic increases the efficiency of operation of the heat sink. Furthermore, this design permits all of the electronics to be interiorly mounted in the sleeve of the motor which provides a unique compact mounting, eliminating any conduit box. Additionally, removal and replacement or repair of the electronic circuitry is easily achieved by disconnecting a few wires, releasing the potting compound with an appropriate method as is known in the art, and removing the heat sink and associated PC board by compressing the heat sink and withdrawing it axially from the motor sleeve. Thus, this heat sink design combines all of the desired characteristics for a heat sink including efficiency of operation, compactness of design, and ease in installation and removal. Furthermore, the heat sink can be constructed of extruded aluminum such that it is easily and cheaply manufactured.
For those motor designs which include a conduit box, the inventor has succeeded in developing a unique mounting arrangement which is not only inexpensive and easily manufacturable, but which also maximizes the operation of the heat sink by exposing the cooling fins to the exterior air. Still another advantage of this heat sink and its mounting is that it is simply and easily installed by deforming tabs cut into the side wall of the conduit box into channels integrally formed in opposite sides of the heat sink. An access hole to each channel permits the insertion of a pin through the channel which forces the tabs back into their preassembled configuration for removal of the heat sink and PC board for repair or replacement. Not only is removal easily accomplished, but the tabs are reusable for replacement of the heat sink and PC board. With integrally formed tabs in the side wall of the conduit box, there is no hardware to be lost or misplaced and additional tabs can easily be cut or punched in the conduit side wall should the original tabs break off. This heat sink design comprises many of the same functional advantages and features in a somewhat different structural arrangement from the first design as it is for use with a conduit box. These functional features include optimal efficiency by exposing cooling fins to exterior air, ease in installation and removal, with repeated removal being possible with the same structure, the elimination of mounting hardware, compact design, and maximum utilization of available space.
Some of the principal advantages and features of the invention have been summarized for convenience above. A fuller understanding of the invention and a complete description thereof is contained in the drawings and description of a preferred embodiment which follows.